In recent years, an alloy, especially an alloy which contains a precious metal such as gold and silver, is drawing an attention as a material which can be used in various applications in the technical fields in which a high technology and a nanotechnology can be applied.
For example, an alloy particle comprising silver and copper is drawing an attention as a material used in an electrically conductive paste, an electrically conductive ink, an electrically conductive fine wiring, and the like; or as a material for a reducing catalyst of carbon monoxide and nitrogen oxides (NOx) as well as for a lead-free soldering and so forth. There is a possibility of controlling characteristics thereof by the ratio of silver to copper in a silver-copper alloy particle; and for example, a silver-copper alloy particle mainly comprising silver, wherein the said particle comprises silver which has superior specific resistance and oxidation resistance and copper which can suppress migration of silver, and a silver-copper alloy particle mainly comprising copper useful as the material for wiring such as a magnet wire are drawing attention. Furthermore, antimicrobial properties of each of silver and copper are drawing attention, and in addition, many applications thereof including use in jewelry are expected; and thus, the silver-copper alloy is a widely wanted material in the industrial world. Migration occurs in many metals, and it is known that silver migrates faster; and it is said that migration thereof can be made slower by alloying it with other metals such as copper. However, silver and copper do not mix homogeneously together, so that in many cases the afore-mentioned characteristics expected as the silver-copper alloy are not fully realized in suppressing the oxidation susceptibility possessed by copper, in suppressing migration of silver, and the like.
Similarly, an alloy particle of silver and nickel is also drawing an attention as a material used in an electrically conductive paste, an electrically conductive ink, an electrically conductive fine wiring, a contact material, an electrode material, a fuse, a catalyst, and the like. There is a possibility of controlling characteristics thereof by the ratio of silver to nickel in the silver-nickel alloy particle; and for example, it is known that even a silver-nickel alloy in the state wherein silver and nickel are not homogeneously mixed not only can express higher corrosion resistance to arc discharge but also can be improved in its heat resistance, abrasion resistance, fusion resistance, catalysis performance, durability as an ignition plug, and so forth, as compared with the silver single body. Therefore, the silver-nickel alloy is a widely wanted material in the industrial world. However, silver and nickel do not mix homogeneously together, so that in many cases the afore-mentioned characteristics expected as the silver-nickel alloy are not fully realized.
Similarly, an alloy particle of gold and nickel is also drawing an attention as a material used in a magnetic sensor, an electrode material, a capacitor, a catalyst, a contact material, and the like. There is a possibility of controlling characteristics thereof by the ratio of gold to nickel in a gold-nickel alloy particle; and for example, it is known that even a gold-nickel alloy in the state wherein gold and nickel are not homogeneously mixed not only can express better performance as a high-reliable electric contact material of electronic parts such as a connector, a small relay, and a printed wire board, but also can be improved in its heat resistance, abrasion resistance, catalysis performance, and so forth, as compared with the gold single body. Therefore, the gold-nickel alloy is a widely wanted material in the industrial world. However, similarly to the silver-copper alloy, gold and nickel form a eutectic body, so that it is difficult to form a homogeneous solid solution. Accordingly, in many cases the afore-mentioned characteristics expected as the gold-nickel alloy are not fully realized.
Further, a silver-antimony alloy has been drawing attention for long as a material used in a recording medium, a low-temperature soldering material, a superconductive material, an electrode material, and the like. There is a possibility of controlling characteristics thereof by the ratio of silver (Ag) to antimony (Sb) in the silver-antimony alloy; and for example, it is known that even a silver-antimony alloy in the state wherein silver and antimony are not homogeneously mixed together can be improved in its abrasion resistance and so forth, as compared with the silver single body. Therefore, the silver-antimony alloy is a widely wanted material in the industrial world. However, silver and antimony form a eutectic body or an intermetallic compound in concentration above a certain level, so that they do not mix homogeneously together. Accordingly, in many cases the afore-mentioned characteristics expected as the silver-antimony alloy are not fully realized.
As discussed above, it is shown that in solid alloys comprising at least two kinds of metals, the two metals exist in various forms; and in an equilibrium diagram thereof, the said at least two metals do not mix together by taking a eutectic body structure or forming an intermetallic compound, whereby making a specific region in which a solid phase is eccentrically located. In such a specific region, the composition ratio of the two or more metals to constitute the alloy in the total alloy is significantly different from the composition ratio of the two metals within an extremely small area with the size in the level of nanometers whereby showing the state of eccentric localization; and as a result, in many cases the characteristics expected as the alloy are not fully realized.
Meanwhile, as to heretofore known production methods of an alloy particle, there are a powder metallurgy method, a liquid phase reduction method, an atomizing method, and the like; however, in fact, the situation today is that there has been no report yet with regard to the metal alloy whose problem of the afore-mentioned eccentric localization has been solved.
For example, as to the producing methods of the silver-copper alloy particle, there are such methods as a liquid-phase reduction method, an atomizing method, and so forth, as described in Patent Document 1, Patent Document 2, and Patent Document 3. However, the silver-copper alloy obtained by any of these methods is a core-shell type or contains a eutectic body; and therefore, there has been no disclosure as to the silver-copper alloy substantially not containing a eutectic body and the producing method thereof. In Patent Document 1, the silver-core and the silver-copper-shell nanoparticle is mentioned, wherein the silver-copper alloy to constitute the shell is described from the elemental analysis in combination of the electron microscopic observation and the energy dispersive X-ray fluorescence measurement. However, because mapping of each of silver and copper in the shell part is not disclosed, and also for other reasons, there still remains the question as to whether or not silver and copper form the solid solution. In Patent Document 4, it is described that silver-covered copper powder obtained by covering the copper particle surface with silver was heat-treated at 150 to 600° C. under the non-oxidative atmosphere thereby dispersing silver to the copper particle to obtain the silver-dispersed copper powder. However, because the silver-dispersed copper powder is produced by dispersing silver metal from the copper particle surface, it is difficult to disperse silver to the central part of the copper particle; and thus, not only it is difficult to have the state not containing the eutectic body in the entire particle thereof, but also the particle diameter thereof is too large to be used as a paste. Moreover, with regard to the analysis method of the silver-dispersed metal powder, there is a possibility that the copper single body might be present in the central part of the particle as it might also be the case that by heat treatment the metal silver that was present as the single body thereof on surface of the copper particle could not be confirmed merely by the surface observation (SEM observation). From these considerations, microscopically the above-mentioned silver-copper alloy cannot be regarded as the alloy, though macroscopically it may be regarded as the alloy.
In addition, there is a method such as for example in which a partial solid solution of the silver-copper alloy particle is obtained by rapidly cooling from the state that the metal silver and the metal copper are co-melted at high temperature; however, there has been no disclosure as to the silver-copper alloy having mainly the non-eutectic body structure such as the solid solution. On top of this, the production thereof requires high energy so that this method automatically leads to problems such as high production cost.
As to the tin-silver-copper alloy, only the eutectic body alloy thereof has been disclosed, as shown in Patent Document 6; and thus, there has been no disclosure as to the metal alloy mainly having the non-eutectic body structure substantially not containing the eutectic body.
As to the production method of an alloy particle of silver and nickel, a powder metallurgy method has been generally used from the past; however, there are such methods as a liquid phase reduction method as shown in Patent Document 7 and an atomizing method as shown in Patent Document 8. However, in the silver-nickel alloys obtained by any of these methods, silver and nickel are not mixed homogenously; and thus, the silver-nickel alloy particle not substantially containing the eutectic body and the production methods thereof has not been disclosed yet. Other than these methods, there is a method in which metal silver and metal nickel are rapidly cooled from the state of the solid solution thereof at high temperature thereby obtaining the solid solution of silver-nickel alloy particle; however, this method requires large energy so that there are problems of a natural tendency to a high production cost and so forth.
As to the production method of an alloy particle of gold and nickel, a powder metallurgy method has been generally used from the past; however, there are such methods as a liquid phase reduction method as shown in Patent Document 9 and an atomizing method as shown in Patent Document 10. However, the gold-nickel alloy in which gold and nickel are mixed homogenously together, especially the gold-nickel alloy particle and the production method thereof has not been disclosed yet. Other than these methods, there is a method in which metal gold and metal nickel are rapidly cooled from the state of the solid solution thereof at high temperature thereby obtaining the solid solution of gold-nickel alloy particle; however, this method tends to make the obtained gold-nickel alloy particle inhomogeneous, and in addition, this requires large energy, so that there are problems of a natural tendency to a high production cost and so forth.
As to the production method of an alloy of silver and antimony, an alloy plating method has been generally used from the past as shown in Patent Document 11. As the different production method from it, there is a method in which an alloy particle of silver and antimony is produced by using a mechanical alloying treatment as shown in Patent Document 12. However, the silver-antimony alloys obtained by these methods contain a eutectic body or an intermetallic compound, so that there has been no disclosure as to the silver-antimony alloy in which these metals are mixed homogenously together.
Besides, there may be such a method in which metal silver and metal antimony are cooled or rapidly cooled from the molten state at high temperature thereby obtaining the partial solid solution thereof; however, there has been no disclosure as to the silver-antimony alloy mainly having a non-eutectic body structure such as a solid solution. Moreover, this method may require large energy to melt them during the time of production thereof; and thus, there is such a problem that the field in which this can be used may not be wide because of a natural tendency to a high production cost and so forth.
In Patent Document 5, which is filed by the present applicant, the producing method of the silver-copper alloy particle is disclosed; however, analysis of the particle obtained by the producing method thereof shown by Example reveals, of the similar kind to later-mentioned comparative examples A1 to A3, that this particle is the silver-copper alloy particle formed of the eutectic body or mixture of single bodies of silver and copper. Accordingly, there has been no disclosure as to the silver-copper alloy substantially not containing the eutectic body, especially as to the solid solution type silver-copper alloy.
The apparatus shown in Patent Document 5 is the one in which fine particles are separated in a thin film fluid formed between at least two processing surfaces which are disposed in a position they are faced with each other so as to be able to approach to and separate from each other, at least one of which rotates relative to the other; and this apparatus is expected to be actively utilized in production of the particles especially with the size in the level of nanometers. Inventors of the present invention tried to produce various nanoparticles by using this apparatus; however, all the relationships between the separation and reaction conditions and the results thereof have not been clarified yet.
Specifically, in the solid metal alloy particles, too, it was confirmed that in the platinum-palladium alloy, the analysis result of the TEM-EDS of one point was almost identical to the ICP analysis result; however, the platinum-palladium alloy was the all proportional solid solution metal as shown in FIG. 4(A). On the other hand, as to the silver-copper alloy, only the silver-copper alloy particle in the state of the eutectic body or of the mixture of the silver single body and the copper single body could be obtained.
More specifically, obtained therein were the silver-copper alloy particles that are similar to those shown in FIG. 54 to FIG. 56. In FIG. 54(A) the STEM-HAADF picture thereof is shown; in FIG. 54(B) the EELS mapping result (Ag) thereof is shown; and in FIG. 54(C) the EELS mapping result (Cu) thereof is shown. Results of FIG. 54 were obtained by using the energy dispersive X-ray analyzer Centurio (manufactured by JEOL Ltd.) and by the atomic resolution analytical electron microscope JEM-ARM 200F (manufactured by JEOL Ltd.) with the acceleration voltage of 200.0 kV and the magnification of 6000000. In FIG. 55(A) the STEM-HAADF picture thereof is shown; in FIG. 55(B) the STEM mapping result (Ag) thereof is shown; and in FIG. 55(C) the STEM mapping result (Cu) thereof is shown. Results of FIG. 55 were obtained by using the Cs corrector-equipped super high resolution STEM analyzer HD-2700 (equipped with EDX) (manufactured by Hitachi High-Technologies Corp.) with the acceleration voltage of 200.0 kV and the magnification of 2200000. In FIG. 56(A) the STEM-HAADF picture thereof is shown; in FIG. 56(B) the STEM mapping result (Ag) thereof is shown; and in FIG. 56(C) the STEM mapping result (Cu) thereof is shown. Results of FIG. 56 were obtained by using the Cs corrector-equipped super high resolution STEM analyzer HD-2700 (equipped with EDX) (manufactured by Hitachi High-Technologies Corp.) with the acceleration voltage of 80.0 kV and the magnification of 2000000.
In the silver-copper alloy particle in FIG. 54, copper is present in center of the particle (core), silver is present around it (shell), and copper is present on surface of the silver-copper alloy particle (average particle diameter of about 20 nm). From FIGS. 54(B) and (C), it can be seen that there are some places where silver or copper is not present, namely, there are some places where 100% of silver is present or 100% copper is present. The silver-copper alloy particle in FIG. 55 is the silver-copper alloy particle (average particle diameter of about 15 nm) in which silver and copper are eccentrically located in the same particle. Especially from (C), it can be seen that there is a place where copper is not present, that is, there is a place where 100% silver is present.
The silver-copper alloy particle in FIG. 56 is the silver-copper alloy particle (average particle diameter of about 15 nm) comprising silver in half of it, namely, 100% silver being present therein, and copper in the other half, namely, 100% copper being present therein in the same particle.
FIG. 57 shows the silver-antimony alloy particle; and in FIG. 57(A) the STEM-HAADF picture thereof is shown; in (B) the STEM mapping result (Ag) thereof is shown; and in (C) the STEM mapping result (Sb) thereof is shown. These were obtained by using the energy dispersive X-ray analyzer Centurio (manufactured by JEOL Ltd.) and by the atomic resolution analytical electron microscope JEM-ARM 200F (manufactured by JEOL Ltd.) with the acceleration voltage of 200.0 kV and the magnification of 6000000.
In this silver-antimony alloy particle (particle diameter of about 20 nm), silver particles having the size of 2 to 5 nm are present in the same particle, wherein there is the place where silver is not present between the silver particles (EDS: 100% antimony).